Electric glass furnace

ABSTRACT

An electric glass furnace in which one or more axially movable electrodes connected to the same terminal project up through the bottom of the furnace and are mounted in special refractory blocks which form platforms above the bottom of the furnace so that electrodes for each terminal are separated by troughs. Also a separate electrode can be provided in the molten glass drawoff riser, which separate electrode may be selectively connected to an opposite terminal of an electrode adjacent the riser in the furnace, grounded, or disconnected. Furthermore, each electrode is sealed in its refractory block by an inert gas, and it and its block are cooled both by a jacket for coolant liquid around the electrode at least partly recessed in the block, and by a blast of cool air from below and against said jacket, the electrode, and the bottom of the block.

United States Patent [72] Inventors William R. Steitz Toledo; Robert 0.Bradley, Ottawa l-lills, both of Ohio; Thomas H. Waterworth, Bridgnorth,Salop, England [2]] Appl. No. 41,385 [22] Filed May 28, 1970 [45]Patented Jan. 11, 1972 [73] Assignees Toledo Engineering Co., Inc.

Toledo, Ohio Elemelt, Ltd. Kingswinford, Brierley, Staffordshire,England, part interest to each [54] ELECTRIC GLASS FURNACE 12 Claims, 5Drawing Figs.

[52] US. Cl 13/6, 65/3 25 [51] Int. Cl C03b 5/02, H05b 3/60 [50] FieldofSearch.....' 13/6, 18; 65/ 325, 326

[56] References Cited UNITED STATES PATENTS 4/1969 Gell etal.

llili GAS FOREIGN PATENTS 664,121 l/l952 Great Britain PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-R. N. Envall, Jr.Attorney-Hugh Adam Kirk trode may be selectively connected to anopposite terminal of an electrode adjacent the riser in the furnace,grounded, or

disconnected. Furthermore, each electrode is sealed in its refractoryblock by an inert gas, and it and its block are cooled both by a jacketfor coolant liquid around the electrode at least partly recessed in theblock, and by a blast of cool air from below and against said jacket,the electrode, and the bottomof the block.

PATENTEU JAN! 1 I972 3,634,588

sum 1 [IF 3 I NV ENTORS WILLIAM R. STEITZ By ROBERT O. BRA DLEY THOMASH. WATER ORT H NEY PATENIED mu I 1972 SHEET 2 BF 3 lNVliNTO/(S WILLIAMR. STE/T2 ROBERT O. BRADLEY THOMAS H. WATE W RTH ATTO N FIG. 3

FIG. 5

ELECTRIC GLASS FURNACE BACKGROUND OF THE INVENTION An example of anelectric glass-resistant furnace of the type involved herein is shown inGell et al. US. Pat. No. 3,440,321 issued Apr. 22, 1969, and previousmethod of cooling the electrodes for such a furnace is shown inBlumenfeld US. Pat. No. 3,39l,236 issued July 2, 1968.

These furnaces are very carefully made of refractory brick so that oncethey are put into operation they will run for several months andpreferably several years before having to be shut down. Thus it isimportant that as little corrosion and erosion as possible takes placeduring the life of the furnace.

Since these are resistance and not arc-type furnaces it is necessaryfirst to melt the glass batch by a combustible fuel to cover the tops ofall electrodes before the current in the electrodes is turned on tomaintain and continue the heating by the resistance of the liquid glassbetween these electrodes. Then the fuel is cut off the top of the moltenglass in the furnace is covered by a layer of unmelted glass batch whichis periodically or continuously maintained by adding it to the top ofthe molten glass as it melts away. Thus the top of the molten glass isprotected from the atmosphere.

SUMMARY OF THE INVENTION Since the most heat generated in the electricalresistance of the molten glass is along the shortest path between theelectrodes, it is desirable that this shortest path to be spaced as faras possible from the bottom surface of the furnace to reduce the erosionon.its refractory bricks and blocks. Accordingly one of the principalfeatures of this invention is to design the bottom of the'furnace sothat between opposite electrodes there are channels or troughs so thatthe shortest distance between electrodes is in the molten glass abovethe bottom of the furnace. In producing these troughs between oppositeelectrodes, the blocks in which the electrodes are mounted are usuallymade of a special type of refractory material, preferably more resistantto erosion than that of the general bricks or blocks of the bottom ofthe furnace, and are built up above the bottom of the furnace so thatthe bases of the electrodes are actually on platforms several inchesabove the bottom floor of the furnace. Since these blocks which made upthese platforms are exposed not only on their upper surfaces adjacentthe electrodes but also along the upper portions of their sides to thehot molten glass, the thermal shock which they are required to resist ismaterially greater. Therefore these platforms are preferably built up insteps, and the edges of their blocks are bevelled so as to reduce asmuch as possible the amount of surface of each block which is in contactdirectly with the molten glass in the furnace.

Furnaces of this type also are provided with molten glass drawoffchannels in their bottoms which feed into risers connected to anotherchamber from which the glass is extracted for manufacture into its endproduct. Often times the amount of glass which is withdrawn from thefurnace during its several months or years of operation, is reduced oreven stopped forawhile. Under such circumstances, unless the glass ismaintained in a molten state in the bottom drawoff channel and risertherefrom, it could solidify and require complete shutting down andrebuilding of the furnace. In order to prevent this a separate electrodeis provided in the riser duct which is connected to theopposite terminalof one of the electrodes adjacent this channel in the furnace itself, soas to provide resistance heating of the molten glass in this channel andriser. This electrode, however, does not necessarily always have to beconnected but should be available in the event that the flow of glassthrough the riser is not sufficient to maintain its temperature or tomaintain it in a molten state. Furthermore when its flow is effective,this same riser electrode may be grounded to prevent stray currents fromthe furnaces electrodes leaking out into the drawoff apparatus from thechamber into which the riser is connected. Still furthermore it may bedesired that neither of these functions for this riser electrode isrequired.

so this riser electrode also should be able to be disconnected entirelyfrom either ground or the electrical energy circuit. Thus a simpleswitch-type mechanism is provided so that all of these functions may beeffected.

Since the electrodes for this particular type of furnace are made ofsintered molybdenum metal and this metal readily oxidizes at above about750 F., it is important that the outside ends of these electrodes bekept below this temperature so as to prevent their oxidation.Furthermore it is important that these electrodes be vertically movableand sealed in their refractory blocks by a gas which would not causetheir oxidation at the point where the temperature of these electrodesgets to and above about 750 F. In this respect each of the molybdenumelectrodes of the furnace are directly jacketed by an inert gas undersufficient pressure so that this gas will purge the cavity between theelectrode block and the electrode. The molten glass along the electrodein the refractory block at some point forms its own seal between theelectrode and the inside of the furnace.

Directly around this electrode and including this inert gas seal thereis provided a cooling liquid jacket which is preferably inserted into acavity or recess in the bottom of the refractory block through which theelectrode extends. By controlling the flow of the liquid such as waterthrough this jac ket, one can cause the natural glass seal at the end ofthe inert gas directly around the electrode to soften so that theelectrode may be vertically moved if it is desired to do so.

In addition to the liquid cooling of the electrodes in their refractoryblocks which in effect also cools their refractory blocks, there hasbeen provided special jets of air which blow against the lower ends ofthe refractory blocks around the electrodes and cooling jackets tofurther cool these parts.

Thus it is not only an object of this invention to improve the qualityof the product and efficiency of an electric heat-resistant-type glassfurnace, but also to reduce the thermal shock on the refractories aroundthe electrodes, increase the life of the furnace by lengthening the heatpath between the electrodes along any surface of the refractories in thebottom of the furnace, and also to allow utilization of the throatelectrode in the drawoff riser from the furnace either for heating orfor grounding stray currents escaping from the furnace.

BRIEF DESCRIPTION OF THE VIEWS The above mentioned and other features,objects and advantages, and a manner of attaining them are describedmore specifically below by reference to embodiments of this inventionshown in the accompanying drawings, wherein:

FIG. 1 is a schematic plan view of an empty resistance electrical glassfurnace showing the electrodes projecting through the bottom thereof,the troughs between these electrodes, the drawofi channel for the moltenglass in the bottom and part of the riser duct therefrom, together withsawtooth electrical resistance lines between opposite terminals of theelectrodes as well as dotted resistance lines from the stray currentswhich also occur between the electrodes of other pairs of terminals;

FIG. 2 is a vertical section taken along jogged line 22 of the bottompart of the furnace in FIG. 1 showing the refractory blocks in which theelectrodes are mounted as well as the trough between them and the bottomdrawoff channel;

FIG. 3 is a section taken line 3-3 of FIG. 1 showing the electrode inthe riser from the drawoff channel, and its electrical connections, aswell as a schematic means for vertically raising and lowering one of theelectrodes in the furnace;

FIG. 4 is an enlarged vertical sectional view through that portion of anelectrode which fits into the refractory blocks at the bottom of thefurnace shown in FIGS. 1, 2 or 3, and which is sealed by an inert gas,and is cooled both by a water jacket and a jet of air as well as thesupports for the jacket; and

FIG. 5 is a sectional view taken along 55 of FIG. 4 showing the bafflesin the water jacket around the electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I Furnace TankConstruction Referring first to FIGS. 1, 2 and 3 there is shown thegeneral outline of a rectangular glass furnace tank having sidewalls andend walls 11 and 12, respectively, and bottom wall 15, all of which aremade of refractory brick. Near the center of the bottom wall 15 andextending part way across it is a lower drawoff channel or trough 16which extends beyond the sidewall 11 through a tunnel 17 into a riser 18into a moltenglass-distributing chamber 19.

One or more clusters of similar electrodes 20 through 27 projectvertically up through the bottom wall 15 into the molten glass in thetank 10, but they do not project above the molten surface of the glasstherein. These electrodes 20 through 27 are relatively equally spacedwith opposite terminals at the ends of the diagonals of two squares onopposite sides of the drawoff channel 16in the bottom of the furnace.For example, the opposite terminal for the group of electrodes 20 is theterminal for the group of electrodes 21, and in the same square,electrodes 22 are opposite electrodes 23. Similarly in the other square,the group of electrodes 24 are electrically oppositely connected toelectrodes 25, and 26 are oppositely connected to electrodes 27.Although three electrodes are shown connected to each of the electricalterminals in this embodiment, one or more may be employed withoutdeparting from the general scope of the invention, except that aspreviously stated, the connection of more than one electrode to eachterminal insures continuous operation in the event one or two of theelectrodes at that terminal fails during the several months or yearsoperation of the furnace. There is also shown schematically fullsawtooth resistance lines diagonally across each square from the centralelectrode of each group to show in what direction the most heatingelectrical current normally flows through the molten glass in the tankwhen it is in operation. Nevertheless there is also some heating currentflow between the electrodes 20 and 23, 20 and 22, 22 and 21, and 21 and23, and similarly for the other square, which currents are shown bydotted sawtooth resistance lines. Thus heat is induced into the moltenglass between all of the different electrode terminals or groups ofelectrodes 20 through 27.

In the riser 18 there is also shown an additional electrode 28 (see alsoFIG. 3) which may be connected by a switch means 30 to one of its threeterminals 31 connected to one end of a transformer 32 which comprisesone of the Scott windings connected at its opposite end via connector 33to the terminals of electrodes 23 adjacent the exit of the drawoffchannel 16 in the tank 10. Under these conditions heating resistancealso occurs between terminals 23 and 28 to maintain the glass liquid inthe tunnel 17 and riser 18, in the event there was very little or noflow therethrough because no molten glass was taken off from the chamber19. During normal operation, however, in order to prevent stray currentsfrom leaving the tank 10, the additional electrode 28 may be connectedto ground 35 via its terminal 36 as shown in full lines in FIG. 3.However, if such ground is not necessary, the switch 30 may be placedinto its Off" or no connection position at terminal 37. Thus, threedifferent possibilities are provided for the connection ofthe additionalelectrode 28 in the riser 18.

Also in FIG. 3 there is schematically shown one of the electrodes 21projecting below the bottom wall of the tank 10 and resting in a socket40 at the upper end of a screw 41 which may be raised and lowered via adrive gear and motor mechanism 42. As previously stated, each one of theseparate electrodes 21 through 28 are so connected to these devices 40,41, and 42 for their vertical movement. There is also shown in FIGS. 3and 4 for the one electrode 21 a clamp means 44 above the socket 40 bywhich the electrical connection is made to this electrode.

Referring back to FIGS. 1 and 2, each of the electrodes 20 through 28 isindividually mounted in separate special refractory blocks 50 or 51,which blocks in turn seat in additional special refractory blocks 52,the upper faces of which blocks 50, 51, and 52 are stepped above thefloor or surface of the wall 15 in the tank 10, so as to providechannels or troughs 55 and 56 which cross each other at the center ofthe squares of the electrodes 20 through 23 and 24 through 27,respectively. The stepped upper edges of the blocks 50, 51, and 52 maybe bevelled at their corners to reduce the amount of the surface that isactually in contact with the molten glass in the tank adjacent theirrespective electrodes. More detail of the seating of the blocks 50 and51 into block 52 is shown in FIG. 4. Thus, the electrodes at eachterminal are raised on platformsabove the bottom surface of the tank sothe electrical resistance between the electrodes connected to differentterminals is shorter directly through the liquid than along the bottomsurface of the tank, thus reducing the amount of heat which is createdon the skin layer of the molten glass against the refractories formingthe surface of the tank and the blocks 51, 52, and 53. Thus, most of theheat from the electrical current goes directly into the molten glass,increasing the efficiency of the operation of the furnace, as well asincreasing the life of the refractories making up its bottom, andspecifically those blocks 50 and 51 supporting the electrodes in thebottom.

[I ELECTRODE MOUNTING AND COOLING Referring now specifically to FIG. 4,there is shown an enlargedportion of a molybdenum electrode, such as forexample electrode 21 although it could be of any one of the otherelectrodes 22 through 28. This electrode portion is shown projectingthrough an aperture 57 in its special refractory block 51, whichaperture is slightly larger in diameter than the outside diameter of theelectrode 21 so that the rod electrode 21 may be vertically movedthrough the aperture 57, but yet the aperture is small enough so thatthe glass in the furnace, when it is cooled sufficiently by the coolingmeans around the electrode 21, will automatically seal it at 58 to theaperture 57 in the block 51. This block 51 is also provided with alarger recess or countersunk section 59 into which is inserted a tubularliquid cooled jacket 60. Between the upper end of this jacket 60 and theend of the countersunk hole 59 there may be provided a cushion gasket ofhighly heat-resistant material 61. However, this material does notcontact the outer surface of the electrode 21 but merely seals the endof the heat exchanger 60 to the bottom of the cavity 59.

This liquid-cooled jacket 60 comprises a pair of concentric inner andouter cylinders 62 and 63 between which liquid, such as water, may bepassed for cooling the electrode 21. In order to insure good circulationof this liquid between these cylinders 62 and 63, baffles 64 areprovided as shown in FIG. 5, which extend diametrically opposite eachother and are spaced from the upper end of the concentric cylinder 62and 63. The lower end of the cylinder 63 is provided with diametricallyopposite inlet and outlet ducts 65 and 66, respectively, the former ofwhich may be valved by means of a valve 67, either in this duct or atanother location remote therefrom, such as in the flexible hoses whichconnect it with the source of the liquid that is passed through thisjacket 60.

Also on opposite sides of the outer cylinder 63 of the heatexchangerjacket 60 there may be provided brackets 68 which are connectedsupporting screws 69 which may be threaded into sleeves 70 permanentlyconnected to the stationary crossbeams 71 under the structure of thefurnace floor. These supporting screws 69 thus also enable a sealingpressure to be placed against the gasket 61 in recess 59 by the upperend of the liquid heat-exchanger jacket 60. Below the jacket 60 there isshown an electrical connection 44 to the electrode 21, as previouslydescribed in connection with FIG. 3.

At the lower end of the jacket 60 and closing its lower end, there maybe provided a ring having a radial aperture 81 and an adjacent clampingring 82 for forcing a flexible gasket 83 into sealing engagement betweenthe rings 80 and 82 and against the outside of the electrode 21. Thisouter ring 82 may be urged to squeeze the gasket 83 by means of bolts 84threaded into the ring 80, of which at least three may be providedcircumferentially of the rings 80 and 82. This seal 83 thus provides anannular fluidtight compartment 85 between the outside of the cylindricalelectrode 21 and the outside of the inner cylinder 62 of the jacket 60so that through the aperture 81 and its tubular connection 86 there maybe forced under pressure an inert gas to protect the electrode 21 belowthe glass seal 58 in the block 51 in the bottom of the furnace 10. Thusif the electrode 21 is to be moved axially and it is sealed at 58 bysolidified glass, all that needs to be done is to reduce the flow ofcooling liquid through the jacket 60 by valve 67 to permit it to warmsufficiently to soften the seal 58 so that the electrode 21 can bemoved, and then once it is in position more coolant can be circulatedagain through the jacket 60 to again form the solid seal 58.

In addition to the inert gas seal 85 between the electrode 21 and theinside of the jacket 60 and refractory block 51, and the liquid coolantthrough the jacket 60, there is also provided a blast of air via theduct 90 which is directed up into the bottom of the blocks 51 and 52 andaround the outside of the jacket 60 and electrode 21 to cool not onlythe outside of the jacket 60 but also the outer and lower ends of therefractory blocks 51 and 52 to reduce the changes of thermal shock. Forexample in one installation, as much as 500 cubic feet of air per minuteis blown on each group of electrodes.

Although the different features of this invention are related, they maybe used separately or in different combinations if desired withoutdeparting from the scope of this invention.

While there is described above the principles of this invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of this invention.

We claim:

1. An electric glass furnace comprising:

A. a melting chamber with sidewalls and a floor,

B. a plurality of electrodes separately axially and vertically movableprojecting above said floor,

C. separate platforms for the electrodes connected to differentelectrical terminals, said platforms being formed of refractory blocksand forming troughs between those electrodes connected to said differentterminals,

D. means for sealing said electrodes in said blocks by an inert gas, and

E. means for cooling each electrode and said blocks forming saidplatforms by both water and air.

2. An electric glass furnace according to claim 1 wherein each saidplatformcomprises a plurality of electrodes.

3. A furnace according to claim 1 wherein each of said platformscomprises a plurality of refractory blocks forming steps from said floorto the top of said platforms.

4. A furnace according to claim 1 wherein said blocks have beveled edgestoward said floor.

5. A furnace according to claim 1 wherein said means for cooling eachelectrode comprises a water-cooled jacket surrounding said electrodebelow said floor.

6. A furnace according to claim 5 wherein said means for sealing saidelectrode in said block also seals said water cooling means surroundingsaid electrode.

7. A furnace according to claim 1 wherein said means for air coolingsaid electrode and blocks comprises a plurality of air 10 jets directedagainst said electrodes and blocks on the outside of said furnace andsaid water cooling means.

8. A furnace according to claim 1 including a riser duct from said floorup outside a wall of said chamber for drawing off molten glass from saidchamber.

9. A furnace according to claim 8 including an electrode in said riserduct connected to a multiple terminal switch having separate connectionsto ground, to the power source of an electrode in said furnace, and to adisconnect position.

10. An electric glass furnace comprising:

A. a melting chamber with sidewalls and a floor,

B. a plurality of electrodes in said furnace projecting above saidfloor, C. a riser duct from said floor extending up outside a wall ofsaid chamber for drawing off molten glass from said chamber, and

D. an electrode in said riser duct connected to a multiple terminalswitch having separate connections to ground, to the power source of anelectrode in said furnace and to a disconnect position.

11. A furnace according to claim 10 wherein said electrodes areseparately axially movable.

12. An electric glass furnace comprising:

A. a melting chamber with sidewalls and a floor,

B. a plurality of electrodes in said furnace separately axially andvertically movable projecting above said floor,

C. separate platforms for the electrodes connected to differentelectrical terminals, said platforms being formed of refractory blocksand forming troughs between those electrodes connected to said differentterminals,

D. a riser duct from said floor extending up outside a wall of saidchamber for drawing off molten glass from said chamber,

E. an electrode in said riser duct connected to a multiple terminalswitch having separate connections to ground, to the power source of anelectrode in said furnace, and to a disconnect position,

F. means for protecting said electrodes in said furnace in said blocksand said electrode in said riser duct by means of an inert gas, and

G. means for cooling each electrode by both water and air includingcooling said blocks forming said platforms.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,634;588 Dated January 11, 1972 Inventor(s) W. R. Stcitz, R..O. Bradleyand 'I. H. Waterworth It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Clolumn 1, line 6, after "and" insert a line 20, after off" .1

insert and line 29, after "path delete to line 72, "furnaces" shouldread furnace Column 2, line 64, after "taken" insert along Column 4,line 61, *after "68" insert to Column 5, line 4, "fluidtight" shouldread fluid tight line 5, "outside" should read inside line 24,

"changes" should read chances Signed and sealed this 6th day of August1971+.

(SEAL) Attest:

MCCOY M. GIBSON, JR. 7 C. MARSHALL DANN Attesting Officer" Commissionerof-Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. ,634,588 Dated January 11, 1972 Inventor(s) W. R. Stcitz, R.O.Bradley and T. H. Waterworth It is certified that error appears in theaboveidentified patent and that said Letters Patent are hereby correctedas shown below:

Clolurnn 1, line 6, after "and" insert a line 20, after ofl" 1 insertand line 29, after '"path' delete to line 72, "furnaces" should readfurnace Column 2, line 64, after "taken" insert along Column 4, line6]., after "68" insert to Column 5, line 4, "fluidtight" should readfluid tight line 5, 'outside" should read inside line 24,

"changes" should read chances Signed and sealed this 6th day of August1971p.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN I Attesting Officer Commissionerof Patents

1. An electric glass furnace comprising: A. a melting chamber withsidewalls and a floor, B. a plurality of electrodes separately axiallyand vertically movable projecting above said floor, C. separateplatforms for the electrodes connected to different electricalterminals, said platforms being formed of refractory blocks and formingtroughs between those electrodes connected to said different terminals,D. means for sealing said electrodes in said blocks by an inert gas, andE. means for cooling each electrode and said blocks forming saidplatforms by both water and air.
 2. An electric glass furnace accordingto claim 1 wherein each said platform comprises a plurality ofelectrodes.
 3. A furnace according to claim 1 wherein each of saidplatforms comprises a plurality of refractory blocks forming steps fromsaid floor to the top of said platforms.
 4. A furnace according to claim1 wherein said blocks have beveled edges toward said floor.
 5. A furnaceaccording to claim 1 wherein said means for cooling each electrodecomprises a water-cooled jacket surrounding said electrode below saidfloor.
 6. A furnace according to claim 5 wherein said means for sealingsaid electrode in said block also seals said water cooling meanssurrounding said electrode.
 7. A furnace according to claim 1 whereinsaid means for air cooling said electrode and blocks comprises aplurality of air jets directed against said electrodes and blocks on theoutside of said furnace and said water cooling means.
 8. A furnaceaccording to claim 1 including a riser duct from said floor up outside awall of said chamber for drawing off molten glass from said chamber. 9.A furnace according to claim 8 including an electrode in said riser ductconnected to a multiple terminal switch having separate connections toground, to the power source of an electrode in said furnace, and to adisconnect position.
 10. An electric glass furnace comprising: A. amelting chamber with sidewalls and a floor, B. a plurality of electrodesin said furnace projecting above said floor, C. a riser duct from saidfloor extending up outside a wall of said chamber for drawing off moltenglass from said chamber, and D. an electrode in said riser ductconnected to a multiple terminal switch having separate connections toground, to the power source of an electrode in said furnace and to adisconnect position.
 11. A furnace according to claim 10 wherein saidelectrodes are separately axially movable.
 12. An electric glass furnacecomprising: A. a melting chamber with sidewalls and a floor, B. aplurality of electrodes in said furnace separately axially andvertically movable projecting above said floor, C. separate platformsfor the electrodes connected to different electrical terminals, saidplatforms being formed of refractory blocks and forming troughs betweenthose electrodes connected to said different terminals, D. a riser ductfrom said floor extending up outside a wall of said chamber for drawingoff molten glass from said chamber, E. an electrode in said riser ductconnected to a multiple terminal switch having separate connections toground, to the power source of an electrode in said furnace, and to adisconnect position, F. means for protecting said electrodes in saidfurnace in said blocks and said electrode in said riser duct by means ofan inert gas, and G. means for cooling each electrode by both water andair including cooling said blocks forming said platforms.